Thread -> pmap (easier to use, them effect)

Gemfile

@@ -7,3 +7,4 @@ gem 'sd_notify'
 gem 'cbor'
 gem 'io-extra'
 gem 'ffi'
+gem 'pmap'

lib/lxc_collector.rb

@@ -4,6 +4,7 @@ require 'pathname'
 require 'prometheus/client'
 require 'lxc'
 require 'ostruct'
+require 'pmap'
 
 require_relative 'ns'
 require_relative 'file-statfs'
@@ -199,8 +200,7 @@ class LxcCollector
       @state.set CTStates[ct.state], labels: labels
     end
 
-    LXC.running_containers.map do |ct|
-      Thread.new ct do |ct|
+    LXC.running_containers.peach do |ct|
       pid, io = CBORIO.popen(:r) {|io| forked2 io, ct }
       begin
         io.map do |l|
@@ -238,7 +238,6 @@ class LxcCollector
         Process.wait pid
       end
     end
-    end.each &:join
     @prometheus
   end